LIFE TESTS ON VACUUM SWITCHES BREAKING 50-KA UNIDIRECTIONAL CURRENT

The results of two different series of life test, carried out on vacuum switches with a self produced axial magnetic field in view of their use in nuclear fusion facilities, are presented. The requirement was to obtain a large number (of the order of 2,000) of interruptions of an unidirectional current of over 50 kA, with a recovery voltage of up to 35 kV. A first series of tests pointed out that the test procedure, with an accelerated life test, was not adequate; in the meanwhile, it was apparent that the contact plate, designed for 50 Hz applications, presented weak points when subjected to extended thermal stresses. Therefore a new version of the switches, with modified contacts, was built. Both the versions of the switches were tested with a new test procedure and the satisfactory results of the tests are presented and discussed.